Unable to establish a trust between the federation server proxy and the Federation Service

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Error:  "Unable to establish a trust between the federation server proxy and the Federation Service. Ensure that the provided credentials are valid credentials for establishing a trust or ensure that the Federation Service address is correct, and then try again"

I saw that all my searches were showing people using self-signed certs.  Are you using them?  If so, you will have to go back to your issuing authority and import its root into your federation proxy.  Fixed it for me.  :)